<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .box {
            position: relative;
            width: 400px;
            border-bottom: 1px solid #ccc;
            margin: 100px auto;
        }

        .box input {
            width: 370px;
            height: 30px;
            border: 0;
            outline: none;
        }

        .box img {
            position: absolute;
            top: 2px;
            right: 2px;
            width: 24px;
        }
    </style>
</head>

<body>
<div class="box">
    <label for="eye">
        <img src="images/close.png" alt="" id="eye">
    </label>
    <label for="pwd">
        <input type="password" name="" id="pwd">
    </label>
</div>
<script>
    // 1. 获取元素
    const eye = document.getElementById('eye');
    const pwd = document.getElementById('pwd');
    // 2. 注册事件 处理程序
    var flag = 0;
    eye.onclick = function () {
        // 点击一次之后， flag 一定要变化
        if (flag == 0) {
            pwd.type = 'text';
            eye.src = 'images/open.png';
            flag = 1; // 赋值操作
        } else {
            pwd.type = 'password';
            eye.src = 'images/close.png';
            flag = 0;
        }

    }
</script>
</body>

</html>
